jpa-2.0

For every @Entity I need to perform the following: public <Entity> boolean insert(final Entity entity){ if (em.find(entity.getClass(), entity.getId()) == null) { et.begin(); em.persist(entity); et.commit(); return true; } return false; } That is persist the entity if it didn't exist, and know if it did or not exist. With Entity I'm trying to reach @Entity, although I realize it's not an inheritance relationship. What class can I use to refer to every JPA entity? I could just create an interface/abstract class MyEntities and have all of them inherit, but is that the way? I'm hoping for less

I want to do something like this: select count(*) from (select ...) (As it would be in SQL), but in JPA. Any ideas on how I would do it? pkainulainen This should do the trick (If you want to use JPA criteria API): CriteriaBuilder cb = getEntityManager().getCriteriaBuilder(); CriteriaQuery<Long> query = cb.createQuery(Long.class); Root<Entity> root = query.from(Entity.class); //Selecting the count query.select(cb.count(root)); //Create your search criteria Criteria criteria = ... //Adding search criteria query.where(criteria); Long count = getEntityManager().createQuery(query).getSingleResult()

I want make a query where I join 2 tables, using the CriteriaBuilder. In MySQL the query I'm trying to make would look like this: SELECT * FROM order LEFT JOIN item ON order.id = item.order_id AND item.type_id = 1 I want to get all orders and if they have an item of type #1, I want to join with this item. However, if no item of type #1 is found, I still want to get the order. I can't figure out how to make this with the CriteriaBuilder. All I know how to make is: CriteriaBuilder cb = em.getCriteriaBuilder(); CriteriaQuery<Order> cq = cb.createQuery(Order.class); Root<Order> order = cq.from

I have inherited a code base on which nearly all relations have the following annotations: @OneToMany(fetch = FetchType.LAZY, cascade = { CascadeType.REMOVE }, mappedBy = "someThing") @OnDelete(action = OnDeleteAction.CASCADE) Now I'm having trouble understanding what @OnDelete does in the first place. Hibernate: OnDelete vs cascade=CascadeType.REMOVE is interesting, but unfortunately doesn't have any answers and the JavaDoc for @OnDelete is particularly worthless. From the other questions it looks like the OnDelete annotation somehow lets the DB do the cascading, while the cascading directive

I'm developing a simple "Book Store" project using Struts 1.3 + JPA (with Hibernate as persistence provider). I cannot switch to Spring or any other more sophisticated development environment (e.g., Jboss) and I cannot use any Hibernate-specific technique (e.g., Session class). Given the fact that I'm in a JSE Environment, I need to explicitly manage the whole EntityManager's lifecycle. The Book entity is defined as follows: @Entity public class Book { @Id private String isbn; private String title; private Date publishDate; // Getters and Setters } I defined three Action classes, which are